LoopTraversal.cpp
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//===- LoopTraversal.cpp - Optimal basic block traversal order --*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/LoopTraversal.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/CodeGen/MachineFunction.h"
using namespace llvm;
bool LoopTraversal::isBlockDone(MachineBasicBlock *MBB) {
unsigned MBBNumber = MBB->getNumber();
assert(MBBNumber < MBBInfos.size() && "Unexpected basic block number.");
return MBBInfos[MBBNumber].PrimaryCompleted &&
MBBInfos[MBBNumber].IncomingCompleted ==
MBBInfos[MBBNumber].PrimaryIncoming &&
MBBInfos[MBBNumber].IncomingProcessed == MBB->pred_size();
}
LoopTraversal::TraversalOrder LoopTraversal::traverse(MachineFunction &MF) {
// Initialize the MMBInfos
MBBInfos.assign(MF.getNumBlockIDs(), MBBInfo());
MachineBasicBlock *Entry = &*MF.begin();
ReversePostOrderTraversal<MachineBasicBlock *> RPOT(Entry);
SmallVector<MachineBasicBlock *, 4> Workqueue;
SmallVector<TraversedMBBInfo, 4> MBBTraversalOrder;
for (MachineBasicBlock *MBB : RPOT) {
// N.B: IncomingProcessed and IncomingCompleted were already updated while
// processing this block's predecessors.
unsigned MBBNumber = MBB->getNumber();
assert(MBBNumber < MBBInfos.size() && "Unexpected basic block number.");
MBBInfos[MBBNumber].PrimaryCompleted = true;
MBBInfos[MBBNumber].PrimaryIncoming = MBBInfos[MBBNumber].IncomingProcessed;
bool Primary = true;
Workqueue.push_back(MBB);
while (!Workqueue.empty()) {
MachineBasicBlock *ActiveMBB = &*Workqueue.back();
Workqueue.pop_back();
bool Done = isBlockDone(ActiveMBB);
MBBTraversalOrder.push_back(TraversedMBBInfo(ActiveMBB, Primary, Done));
for (MachineBasicBlock *Succ : ActiveMBB->successors()) {
unsigned SuccNumber = Succ->getNumber();
assert(SuccNumber < MBBInfos.size() &&
"Unexpected basic block number.");
if (!isBlockDone(Succ)) {
if (Primary)
MBBInfos[SuccNumber].IncomingProcessed++;
if (Done)
MBBInfos[SuccNumber].IncomingCompleted++;
if (isBlockDone(Succ))
Workqueue.push_back(Succ);
}
}
Primary = false;
}
}
// We need to go through again and finalize any blocks that are not done yet.
// This is possible if blocks have dead predecessors, so we didn't visit them
// above.
for (MachineBasicBlock *MBB : RPOT) {
if (!isBlockDone(MBB))
MBBTraversalOrder.push_back(TraversedMBBInfo(MBB, false, true));
// Don't update successors here. We'll get to them anyway through this
// loop.
}
MBBInfos.clear();
return MBBTraversalOrder;
}